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Belonging to,or concerning, a focus; as, a focal point. Focal distance, or length,of a lens or mirror (Opt.), the distance of the focus from the surface of the lens or mirror, or more exactly, in the case of a lens, from its optical center. --Focal distance of a telescope, the distance of the image of an object from th…

The act of focalizing or bringing to a focus, or the state of being focalized.

To bring to a focus; to focus; to concentrate. Light is focalized in the eye, sound in the ear. De Quincey.

Having two foci, as some spectacle lenses.

Having the same foci; as, confocal quadrics.

With the lower focal points all in the same plane; -- said of sets of eyepieces so mounted that they may be interchanged without varying the focus of the instrument (as a microscope or telescope) with which they are used.

of a converging lens and a diverging lens of equal and opposite astigmatism but different focal lengths, and sensibly free from astigmatism.

lens, in consequence of which the rays derived from one point are not brought to a single focal point, thus causing imperfect images or indistictness of vision.

Specifically, having such a combination of concave and convex sides as makes the focal axis the shortest line between them. See Illust. under Lens.

ns used as a condenser. -- Bull's-eye condenser, or Bull's-eye (Optics), a lens of short focal distance used for concentrating rays of light. -- Injection condenser, a vessel in which steam is condensed by the direct contact of water. -- Surface condenser, an apparatus for condensing steam, especially the exhaust of…

cording to the metric system; a refractive power equal to that of a glass whose principal focal distance is one meter.

ned toward the object glass, and separated from each other by about half the sum of their focal distances, the image viewed by the eye being formed between the two lenses. it was devised by Huyghens, who applied it to the telescope. Campani applied it to the microscope, whence it is sometimes called Campani's eyepiece.…

To bring to a focus; to focalize; as, to focus a camera. R. Hunt.

of a satellite; -- opposed to emersion. Immersion lens, a microscopic objective of short focal distance designed to work with a drop of liquid, as oil, between the front lens and the slide, so that this lens is practically immersed.

the limits of distincts vision in different individuals, and thus determiming the proper focal length of a lens for correcting imperfect sight. Brande & C.

smic vertical, the point upon the earth's surface vertically over the center of effort or focal point whence the earthquake's impulse proceeds, or the vertical line connecting these two points.

An instrument of such focal length that it may be used as an observing telescope for objects close at hand or as a long-focused microscope.

cially designed to give a large image of a distant object in a camera of relatively short focal length.

The reciprocal of the focal distance of a lens, used as measure of the divergence or convergence of a pencil of rays. [R.] Humphrey Lloyd.